The present invention relates to a mass analysis system for detecting explosives, hazardous materials and narcotics.
As conventional art methods for effecting detection to determine whether there are explosives, hazardous materials and narcotics, there are chemiluminescence, ion mobility analysis, and mass spectrometry.
In the chemiluminescence, subject vapor is picked, temporarily adsorbed on a filter to concentrate. Then the vapor is heated to leave the filter and decomposed by using gas chromatographs, and reacted with a reagent to detect emission of light (first conventional art: U.S. Pat. No. 5,092,155).
In the ion mobility analysis, subject gas is absorbed in, adsorbed on a filter to concentrate, and heated to decompose. The subject gas is then ionized with a radioisotope contained in an ion source. The ions are injected into a drift tube, and the mobility of ions is detected (second conventional art: U.S. Pat. Nos. 4,987,767 and 5,109,691).
As a highly sensitive detection system capable of detecting an extremely small amount of trace, an atmospheric pressure chemical ionization source with counter-flow introduction has been reported (third conventional art: JP-A-2001-093461).
There is reported a mass analysis system that measures the temperature of an ion source is measured immediately after power turning on, and conducts control so as to start an exhaust device only in the case where its temperature is at least a predetermined preset value and so as not to start the exhaust device in the case where its temperature is lower than the preset value (fourth conventional art: JP-A-9-45277). In the fourth conventional art, the exhaust device is controlled in order to hold down damage such as oxidation the high temperature ion source suffers to the minimum.
There is reported a mass analysis system having control means for controlling exhaust means (exhaust means having a variable exhaust capability for vacuum-exhausting an analysis chamber) so as to lower the exhaust capability during an interval that an analysis is not being executed or during an interval that it is not necessary to maintain a high vacuum state and so as to raise the exhaust capability to restore the high vacuum state when a certain analysis is started (fifth conventional art: JP-A-2000-36283). It is described that the fifth conventional art has an effect that the electric power of the exhaust means as a whole can be reduced and the running cost can be saved.
In the method of the first conventional art, the subject substance is previously separated by using gas chromatograph. Therefore, the method is extremely high in sensitivity and selectivity with respect to a specific subject substance. However, it is necessary to temporarily collect and trap vapor from the subject substance, then carry the concentrated substance to a measurement device of installed type and effect detection. Furthermore, there is a problem that it is necessary to effect separation by using a gas chromatograph in order to raise the sensitivity and it takes time until detection.
In the method of the second conventional art, it is possible to detect a subject substance in a short time by collecting and trapping vapor from the subject substance with an absorber, concentrating the vapor, and then effecting decomposition again. Since all absorbed substances are ionized, however, the ionization efficiency of a specific substance is lowered and the detection sensitivity is low. Furthermore, there is a problem that separation in the drift tube is difficult and the selectivity is low.
The system of the third conventional art is capable of absorbing vapor from a subject substance on line, detecting the vapor with high sensitivity, and operating continuously. If a mass analysis system using an atmospheric pressure chemical ionization source is used as a detection system as in the third conventional art, then selective ionization of a specific substance is possible, and the sensitivity especially to a nitro-compound, which is a main component of explosives, is high. Thus, it is possible to detect at the room temperature plastic explosives, which has been conventionally difficult to detect in the gas state because of its low vapor pressure. Furthermore, since the sensitivity is extremely high, on-line detection can be achieved without using pre-processing, such as collection of the subject substance using a filter and concentration, and measurement in a short time is possible. Furthermore, by conducting pre-processing, the detection sensitivity is further improved and the subject substance can be detected.
The system of the third conventional art is basically installation type, and it can be applied to X-ray imaging detection systems and security gates. However, the system of the third conventional art has a problem that its application is difficult when detecting a doubtful article or when the necessity of an urgent detection inspection has occurred. In the case of such detection of a doubtful article, there is a problem that it takes time because vapor is acquired by using a small-sized absorption machine of vacuum cleaner type and measurement is conducted by a system of installation type. In other words, the merit of the system of installation type that an on-line measurement is possible cannot be made the most of.
At the time of emergency such as when a doubtful article has been found, it is necessary in an explosive detection system to rapidly determine whether the doubtful article is an explosive. Furthermore, it is desirable that an extremely small amount of trace can be detected with high sensitivity and high selectivity. In addition, it is desirable that the start time is as short as possible in order to be transportable, simply movable and then measurable rapidly.
On the other hand, for raising the detection sensitivity of a mass analysis system used in an explosive detection system that can cope with an emergent inspection, it is an important subject to lower the background caused by adsorption of the detection subject substance into pipe laying or adsorption of impurities. For preventing the background from rising, it becomes necessary to use a substance that is hard to absorb gas as a material of the pipe laying and heat the pipe laying.
However, there is a fear that the highest electric power will be exceeded when measurement start of a mass analysis system, start of an exhaust device and pipe laying heating start are simultaneously executed. Especially in the case of the exhaust device, electric power immediately after the start is high in many cases because of characteristics of the device. In the case where the above starts are executed simultaneously, therefore, the mass analysis system cannot be used with a typical home power supply. For making use of a typical home power supply possible, it is necessary to heat the pipe laying after starting the exhaust device and then sufficiently effecting the exhaust. Since in this case it takes an extremely long time for the pipe laying to arrive at a predetermined temperature as a result of pipe laying heating, the start time as a whole becomes long.
Furthermore, in a conventional mass analysis system serving as a chemical analysis system, it is necessary to bring mainly its ion source and detector to a high vacuum state. After a sufficient vacuum state has been reached, the temperature is raised. Especially when effecting an analysis of an extremely minute amount, it is desired to implement as high vacuum state as possible because mixture of impurities into the ion source is disliked. When the pipe laying is heated in the state of the atmospheric pressure, there is a fear that the inside of the pipe laying or the inside of the ion source will be oxidized. Therefore, heating is typically executed in the high vacuum state.
In a conventional mass analysis system serving as a chemical analysis system, the necessity for reducing the electric power and the start time mainly in the system of installation type is not great. At the time of start, it is typical that a vacuum exhaust device is initialized and then processing such as various kinds of heating is executed. Thus in the mass analysis system serving as a conventional chemical analysis system, various kinds of heating is executed after vacuum exhaust. Therefore, the start time becomes long because of heating requiring the longest time.
In the conventional typical transportable analysis system, initialization of the system is effected by using a method similar to that of the system of installation type. The reason will now be described. In the analysis system, it is necessary to analyze the detection subject substance with high precision. If analysis is not executed when a sufficient high vacuum state is achieved by the vacuum exhaust, a measurement result might depend upon impurities contained in the atmosphere.
In a transportable explosive detection system, it is necessary to start rapidly the system after a movement of the system and effect detection. In addition, it is necessary to suppress the maximum electric power in order to use the system with an ordinary home power supply.